Radiation Synthesis and Characterization of Conducting Polyaniline and Polyaniline/Silver Nanoparticels

Abstract

The conducting polymer PANI nanoparticles were synthesized from polyvinyl
alcohol PVA and aniline hydrochloride (AniHCl) blend films at different AniHCl
monomer concentrations (0.5, 1.0, 1.5 and 2.0 g or as 9.0, 16.7, 23.1, and 28.6 wt %)
and irradiated with gamma radiation at different doses (0, 10, 20, 30, 40, and 50
kGy) at ambient conditions. Upon irradiation AniHCl undergoes dechlorination by
the loss of Cl– that acts as an oxidant and ‘in situ’ polymerizing aniline into
conducting PANI nanoparticles. The formation of conducting PANI has been
observed by the change of colour from colourless to dark green due to the formation
of polaron species characterized by the defect in molecular structure of the polymer
and was confirmed by Raman scattering at 1637 cm-1 Raman shift assigned for C=N
stretching of imines group. The SEM morphology of PVA/PANI composites reveals
the spherical structure of nanoparticles, 50 – 100 nm in diameter which then transformed into globular clusters of conducting PANI with good environmental
stability.
The optical properties of PANI nanoparticles were measured by means of UV-visible
spectrophotometry and found that the absorbance at 790 nm band of conducting
PANI increased exponentially with the increase of dose and fitted the expression of
the form: exp( / ) 0 0 y y D D , where D is the absorbed dose and 0 D is the dose
sensitivity. The results reveal that the optical parameters such as absorption edge,
activation energy, and band gap energy decreased with the increase of dose and
AniHCl concentration. When the dose increased from 10 kGy to 50 kGy the
absorption edge decreased from 1.0 to 0.91 eV for 9.0% AniHCl and from 0.82 to
0.44 eV for 28.6% AniHCl, the activation energy decreased from 2.25 to 1.5 eV for
9.0% AniHCl and from 0.8 to 0.69 eV for 28.6% AniHCl, and the band gap energy
decreased from 1.36 to 1.18 eV for 9.0% AniHCl and from 1.12 to 1.00 eV for 28.6
wt% AniHCl. The electrical conductivity was determined by an impedance analyzer
and found the conductivity increased with the increase of dose and AniHCl
concentration. The conductivity is mainly the direct current (dc) component
attributed to the creation of polarons in the PANI structure and they are the charge
carriers of conducting PANI which are set in motion in a form of electron hopping
within the backbone of the composites. The dc conductivity increased from
5.75106S/m to 1.32 103 S/m for 9.0 wt% and from 7.76105 S/m to
1.17 10 1 S/m for 28.6 wt% AniHCl when the dose was increased from 10 kGy to
50 kGy. The dc conductivity is therefore governed by the exponential relation of the
form: exp( / ) 0 0 D D dc   , where 0  and 0 D were found varied with different
AniHCl concentration.The silver nanoparticles were synthesized from PVA/silver nitrate (AgNO3) blend
films at different AgNO3 dopant concentration of 0.01 wt % and irradiated with
gamma radiation at different doses (0, 10, 20, 30, 40, and 50 kGy) at ambient
conditions. Upon gamma irradiation, the released electrons interact with silver ions
Ag+ which reduce to silver nanoparticles Ag0. The formation of Ag0 nanoparticles
has been observed by the colour changed from colourless to golden yellow due to the
presence of Ag0 nanoparticles and was confirmed by XRD analysis. Further, the
presence of metal nanoparticles was verified with the UV-visible absorption
measurement that reveals the absorption peak at 425 nm due to surface plasmon
resonant phenomenon at the conduction band of Ag0 nanoparticles where the
absorbance increased with the increase of dose and fitted the expression of the form:
exp( / ) 0 0 y y D D .
The composites of PVA/PANI/Ag0 nanoparticles were radio-synthesized with the
concentration of AniHCl at 28.6 wt%. The concentrations of AgNO3 dopant are
different (0.01, 0.03, 0.05, and 0.07 wt %) and different radiation doses (0, 10, 20,
30, 40, and 50 kGy). The results from optical absorption measurement reveal two
absorption bands at 415 nm due to surface plasmons of Ag0 nanoparticles and at 600
nm due to polarons of low conducting PANI. The absorption band shifted from 425
nm to 415 nm crrosponds to decreasing diameter of Ag0 nanoparticles in the presence
of PANI in the composites. The band gap increased with the increase of AgNO3
dopant, from 1.72 eV for 0.01 wt% to 2.58 eV for 0.07 wt% dopant irradiated at 50
kGy. The dc conductivity increased with the increase of dose and decreased with the
increase of dopant concentration Ag+. The dc conductivity for 0.01 wt% dopant
increased from 9.77 106 S/m at 10 kGy to 8.51104S/m at 50 kGy. For dopant concentration at 0.07 wt%, however, the dc conductivity increased from
1.07 10 7 S/m at 10 kGy to 1.23 105 S/m at 50 kGy. The dc conductivity of
PVA/PANI/Ag0 nanocomposites was found to have an exponential expression of the
form: exp( / ) 0 0 D D dc   .